TGF-β1 and TIMP-4 regulate atrial fibrosis in atrial fibrillation secondary to rheumatic heart disease

To investigate the involvement of transforming growth factor-beta 1 (TGF-beta 1) and tissue inhibitor of metalloproteinase 4 (TIMP-4) in influencing the severity of atrial fibrosis in rheumatic heart disease (RHD) patients with atrial fibrillation (AF). The degree of myocardial fibrosis was evaluated using Masson staining. The expression levels of TGF-beta 1, TIMP-4, matrix metalloproteinase-2 (MMP-2), type I collagen, and type III collagen were estimated by Western blot analysis. Additionally, TGF-beta 1 and TIMP-4 mRNA levels were quantified by qRT-PCR. The effect of TGF-beta 1 stimulation on TIMP-4 expression was assessed by in vitro stimulation of freshly isolated human atrial fibroblasts with recombinant human TGF-beta 1, followed by Western blot analysis to detect changes in TIMP-4 levels. Masson stain revealed that the left atrial diameter and collagen volume fraction were obviously increased in AF patients, compared to sinus rhythm (SR) controls (both P < 0.05). Western blot analysis showed significantly elevated levels of the AF markers MMP-2, type I collagen, and type III collagen in the AF group, in comparison to the SR controls (all P < 0.05). In the AF group, TGF-beta 1 expression was relatively higher, while TIMP-4 expression was apparently lower than the SR group (all P < 0.05). TIMP-4 expression level showed a negative association with TGF-beta 1 expression level (r = -0.98, P < 0.01) and TGF-beta 1 stimulation of atrial fibroblasts led to a sharp decrease in TIMP-4 protein level. Increased TGF-beta 1 expression and decreased TIMP-4 expression correlated with atrial fibrosis and ECM changes in the atria of RHD patients with AF. Notably, TGF-beta 1 suppressed TIMP-4 expression, suggesting that selective TGF-beta 1 inhibitors may be useful therapeutic agents.